<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{margin: 0;padding: 0}
        #wrap{
            margin: 30px;
            width: 400px;
            height: 400px;
            border: 1px solid;
            position: relative;
        }
        #inner{
            position: absolute;
            width: 100px;
            height: 100px;
            background: pink;
        }
    </style>
</head>
<body>

<div id="wrap">
    123
    <div id="inner"></div>
</div>

<div style="height: 10000px"></div>
</body>
</html>